This invention relates to a centrifugal angular advance device for internal combustion engines, particularly to improvements on weights used in the centrifugal angular advance device.
Generally, the centrifugal angular advance device comprises a base plate secured to a rotary shaft driven by an engine, a pair of weights arranged on the base plate symmetrically with respect to an axis of the base plate, and an advance member engaged with the pair of weights so that the advance member will angularly advance relatively to the base plate when rotating. The advance member is provided thereon with a cam or magnetic rotor which actuates an ignition circuit for the internal combustion engines, as well known.
Each weight of the pair of weights has a drive pin rigidly fixed thereto which drives the advance member to provide an angular advance of the advance member according to rotation of the base plate. It is necessary for the advance member to make a smooth movement. Therefore, the drive pin is required to have hard and smooth face which is in contact with the advance member.
There are known weights in which first, precisely finished drive pins are fixed to the weights, then the drive pins are subjected to cementation and quenching. Thus produced weights have a defect that precisely finished drive pins are roughed. In the centrifugal angular advance device in which the cam is provided, an amount of lagging in the relative angular movement of the advance member which is brought by contact of the advance member and roughed drive pins, is relatively small because the advance member is forced to move by shocks due to contacting and breaking of contacts of the ignition circuit. On the other hand, in the centrifugal angular advance device in which the magnetic rotor is provided, which is so-called, of non-contact type, the lagging becomes large as compared with the above-mentioned device, because there is no shock in this device.
Further, there are known centrifugal angular advance devices in which drive pins provided in weights each have a ball bearing, for example by Japanese Open-laying of Patent Application No. 79838/76 and Japanese Patent Publication No. 36403/76. By provision of the ball bearing, sticking or lagging has been extreamly improved.
The drive pin with the ball bearing is press-fitted in the weight hardened. A hole of the weight made for the drive pin must be precisely finished, but the hardening causes the precisely finished hole to deform. When the press-fitting is effected under the deformation of the hole, strong fitting is not expected, or cracking of the weight may be produced. Therefore, it is necessary to correct the deformation of the hole by precisely finishing it. Usually, the precise finishing of the hole after the hardening is carried out by grinding or honing. However, as the diameter of the drive pin with the ball bearing is small, it is difficult to grind the hole of such a small diameter. The grinding or horning of such small hole is not suitable for mass production because of much time comsumption. Further, even if the hole is precisely finished, some of the weights may accompany cracks thereof when the drive pins are pressfitted.